SELECTOR VALVE

Abstract: A selector valve includes an annular body having a sealing surface (22) having a plurality of inlet ports (24). The sealing head (25) carries a seal member (29) which is urged by a spring (30) against the surface (22). The seal member (29) has a sealing face cmprising a central band (31) and lateral area (32 and 33) above and below the band (31). The lateral areas (32 and 33) are reduced in size compared to the area of the band (31).

Description: Selector Valve This invention relates to a selector valve which may be used to from a single input to a plurality of outputs. Although the invention will be primarily described in relation to a sampling valve which can take fluid flowing from any of a plurality of inlets and direct it to a single outlet, it will be appreciated that the invention is equally applicable to a distributor valve arrangement acting in the opposite way and to comparable structures and devices. Typical known selector valves are describe in GB 995016D, US 4191213B, US 5046522B, WO87/02428 and US 41989641B. In the prior known valves, for example the valve described in 087/02428, and also in the known valve shown in figures 1, 2 and 3 a known selector valve 10 has a plurality of selectable ports 11 each terminating at a sealing surface 12 which forms a path for and is slidingly engaged by a selector head 13 whose port 14 is surrounded be a seal member 15 urged against a surface 12 as by a spring 16. Referring now to figures 2 and 3 it will be seen that as the seal member 15 traverses the mouths of the ports 11 in use there is a degree of wear over that central band 17 which engages the edges of the mouths of the ports 11. After some use that central band 17 tends to become more worn than the remainder of the seal member 15 and this wear is shown (in an exaggerated manner) as a central groove 18 in figure 3. It will be appreciated that the groove 18 effectively provides a leak path in the direction of arrow 19. It will be appreciated that comparable problems will arise in relation to similar selector valves, for example the selector valve described in specification GB995016B wherein the selector head moves over a flat surface rather than over a cylindrical surface. It is an object of the invention to provide an improved selector valve. The invention provides a selector valve having a plurality of selectable ports terminating at mouths in a sealing surface which can be traversed by a selector head having a seal member which provides a seal between a selected port and a port of the selector head, the seal member having, considered in its direction of travel relative to the selectable ports a central band which traverses those ports and lateral portions which do not traverse the ports, the areas of said lateral portions being selected so that the wear which they undergo during their traversing of the sealing surface without contact with the selectable ports is generally equal to the rate of wear of the central band which traverses the ports. The invention also provides a selector valve having a plurality of selectable ports terminating at mouths in a sealing surface which can be traversed by a selector head having a seal member which provides a seal between a selected port and a port of the selector head, the seal member having, considered in its direction of travel relative to the selectable ports a central band which traverses those ports and lateral portions which do not traverse the ports, wherein the area of the lateral portions of the seal member are smaller than the area of the central band so as to wear at about the same rate as the central band. The invention further provides a selector valve having a plurality of selectable ports terminating at mouths in a sealing surface which can be traversed by a selector head having a seal member which provides a seal between a selected port and a port of the selector head, the seal member having, considered in its direction of travel relative to the selectable ports a central band which traverses those ports and lateral portions which do not traverse the ports, wherein the areas of the lateral portions of the sealing face of the seal member are reduced so as to wear at about the same rate as the central band. As it will be appreciated, the seal member has in the past generally been selected to be circular to uniformly surround the selected ports on the selector surface. In carrying out the invention it is possible for the circular seal member to be reduced in width in a direction transverse to its path of travel by having flats formed on it. Alternatively an elliptical shape can be chosen having its longer axis in the direction of travel. A further problem arises in relation to such selector valves in the provision of a seal between a stem of the selector head and a static part of the valve. The selector head is usually mounted on the end of a (for example) "L" shaped length of ducting, one limb of which effects simple pivoting about its axis and the other of which carries the sealing head at its end. The first limb, at its end, must be sealed relative to static structure such as pipe work which will direct the selected input to, for example, analytic equipment. It will be appreciated that for analytic equipment a high integrity rotary seal must be provided between the static parts and the rotating limb of the selector head. It is a further object of the invention to improve such a selector valve by reducing the standards required for an effective seal at that position. The invention further provides a selector valve including a selector head comprising ducting in having a first part which rotates about its axis and a second part which carries a selector seal at its free end, the free end of the first part being sealed against non-rotating structure by an annular sealing ring, wherein a static tube extends into the first part of the ducting. The provision of the static tube enables samples to be taken from flow within the ducting upstream of the sealing ring thus making any leak at the sealing ring of lower significance. The portion of the ducting surrounding the tube can lead to an exhaust vent via the sealing ring. The invention also provides a sampling arrangement including a selector valve as aforesaid and including a plurality of sample sources capable of causing a given flow rate in the selector head conduit and in combination with destination equipment having a flow requirement less than flow rate in the selector head ducting, excess flow in the ducting being allowed to pass outside the selector tube passed through the annular seal between the end of the ducting and static parts and be vented to waste. The destination equipment can be analytic equipment such as a gas chromatograph. The invention will be described further, by way of example, with reference to the accompany drawings wherein: Figure 1 is a plan view of a known selector valve; Figure 2 is an end elevation of a seal member of a selector head of the valve of figure 1; Figure 3 is a perspective view of the seal member; Figure 4 is a cross-sectional view of the selector of figure 1 modified in accordance with the invention; Figure 5 is a view similar to figure 2 but showing the invention; Figure 5a is an enlarged view of figure 5; Figure 5b is a perspective view of figure 5; Figure 6 is a view similar to figure 5 but showing a variation; Figure 7 is a cross-sectional view of selector valve; Figure 8 is a view similar to figure 7 but showing the selector valve of figure 7 modified in accordance with a second feature of the present invention; Figure 9 shows a modification to the selector valves shown in figures 5, 6 and 7; and Figure 10 shows to an enlarged scale a detail of the modification shown in figure 9; and Figure 11 shows a modification to the arrangements shown in figures 7 and 8. Referring now to figures 4 and 5 it will be seen that instead of the arrangement of figures l, 2 and 3 (which has already been described) a preferred valve of the invention has an annular body 21 providing a circular sealing surface 22 into which open the mouths 23 and a plurality of selectable inlet ports 24. A sealing head 25 includes one limb 26 of selector ducting 27 whose other limb 28 is disposed on and rotatable about an axis of the valve. The selector head 25 carries a seal member 29 which is urged by a spring 30 against surface 22 and has a sealing face which is shown in figure 5. As best seen in figure 5a the sealing face of the seal member 29 has a central band 31 which, in use, traverses the mouths 24. Lateral areas above and below the band 24 are indicated at 32 and 33. As best seen in figure 5 the lateral areas 32 and 33 are reduced in size compared to the areas of the band 31. The reduction in size is such that the area of the band 31 (ignoring the central aperture communicating with the ducting 26) is greater than the areas 32 and 33. This reduction in the size of the areas 32 and 33 means that the contact pressure imposes greater wear on the areas 32 and 33 during the sliding movement with the surface 22. Thus, in use the central band 31 and the areas 32 and 33 wear in unison and the groove illustrated at 18 in figure 3 does not develop. Or, if it does, only develops after a prolonged period of use at which stage the seal can be replaced. The valve 20 of figure 4 is more completely described in figure 7 and it will be seen that the sealing head 25 forms part of a distributor whose porting has a limb 28 sealed by annular seal 34 to part of a housing 35 to which is connected pipe work 36 which can lead to destination equipment, for example analytic equipment such as a gas chro atograph. The selector head is rotated by means of a shaft 37 and non-selected ports 11 vent to the interior 38 and exit via exhaust port 39. It will be appreciated that the interior of the housing 35 illustrated at 40 will be filled with un-selected fluid streams and therefor the integrity between the ducting 28 and that interior must be maintained quite highly by the seal 34. Any leakage through the seal 34 could cause entry of fluid into the sample. Figure 8 illustrates how, in accordance with a second feature of the invention the danger of leakage at the seal 34 can be significantly reduced. Here, a sampling tube 41 passes fixedly through the pipe work 36 and enters telescopically into the ducting 27. The tube 41 lies on the axis of rotation of the selector head and therefore is a static item. The free end 42 is well upstream (considered in the direction of flow of sampled product) and therefore the product to be sampled enters via the open ended tube 42 passes down tube 41 and passes to its use destination. Excess flow carries on in the annular space 43 to exhaust. It will be appreciated that any leakage at the seal 34 does not affect the sample selected because it will be virtually impossible for any contaminant to pass, to the left in figure 8, from the seal 34 towards the inlet 42 against the flow in the space 43. This allows the seal 34 to be an item of less expensive and less critical construction and its inspection and maintenance, although necessary, can be reduced in frequency and therefore in cost. Referring to figures 9 and 10 there is shown a modification which can be applied to the selector valves shown in figures 4, 5, 6, 7 and 8. Components similar to those in the previous figures have been accorded identical reference numbers. The spring (30) seats at one end against a shoulder (44) provided on the limb (26) . The opposite end of the spring (30) seats against an inner sealing ferrule (45) which is mounted on the limb (26) and positioned within a recess (46) within the seal member (29) . The function of the sealing ferrule (45) is to prevent leakage along the path formed between the external diameter of the limb (26) and the internal diameter of the sealing member (29) . This leakage increases with temperature due to the differential thermal expansion rates of the seal member which is formed from PTFE and the stainless steel limb (26) . The load exerted by the spring (30) acts on the sealing member (29) via the sealing ferrule (45) ♦ This spring loading forces the lip (45A) of the ferrule into inti iate contact with the sealing member (29) and the limb (26) so forming a sliding seal. The sealing takes place at a point very close to the open mouth of the port face and thus minimises accumulation of sample material trapped in the path mentioned above. Referring to figure 11, the sealing ferrule (45) is shown being urged into contact with the sealing member (29) by the spring (30) which bears at one end against a seating (47) provided on the shaft (37) and the limb (26) extends through a duct (48) formed in the shaft (37) . The invention is not limited to the precise details of the foregoing and variations can be made thereto. Clearly the invention is applicable to both distribution and selector valves (apart from the second feature thereof) but both inventions are relevant to selector valves wherein there is either distribution or sampling and wherein the selector head moves over a flat, conical or other surface into which extend a number of mouths of selectable ports. Many other variations are possible within the scope of the invention.

Claims: Claims 1. A selector valve having a plurality of selectable ports terminating at mouths in a sealing surface which can be traversed by a selector head having a seal member which provides a seal between a selected port and a port of the selector head, the seal member having, considered in its direction of travel relative to the selectable ports a central band which traverses those ports and lateral portions which do not traverse the ports, the area of said lateral portions being selected so that the wear which they undergo during their traversing of the sealing surface without contact with the selectable ports is generally equal to the rate of wear of the central band which traverses the ports. 2. A selector valve as claimed in claim 1 having a plurality of selectable ports terminating at mouths in a sealing surface which can be traversed by a selector head having a seal member which provides a seal between a selected port and the port of the selector head, the seal member having considered in its direction of travel relative to the selectable ports a central band which traverses those ports and lateral portions which do not traverse the ports, wherein the areas of the lateral portions of the seal member are smaller than the area of the central band so as to wear at about the same rate as the central band. 3. A selector valve as claimed in claim 1 having a plurality of selectable ports terminating at mouths in a sealing surface which can be traversed by a selector head having a seal member which provides a seal between a selected port and the port of the selector head, the seal member having considered in its direction of travel relative to the selectable port a central band which traverses those ports and lateral portions which do not traverse the ports, wherein the areas of the lateral portions of the sealing face of the seal member are reduced so as to wear at about the same rate as the central band. 4. A selector valve as claimed in any one of the preceding claims in which the circular seal member is reduced in width in a direction transverse to its path of travel by having flats formed on it. 5. A selector valve as claimed in any one of the preceding claims 1 to 3 in which the circular sealed member is generally elliptical cross section having its longer axis in the direction of travel. 6. A selector valve as claimed in any one of the preceding claims including a selector head comprising ducting having a first part which rotates about its axis and a second part which carries a selector seal at its free end, the free end of the first part being sealed against a non-rotat structure by an annular sealing ring wherein a static t extends into the first part of the ducting. 7. A selector valve as claimed in claim 6 in which the port of the ducting surrounding the tube leads to an exha vent via the sealing ring. 8. A selector valve as claimed in any one of the preced claims including a plurality of sample sources capable causing a given flow rate in the selector head conduit in combination with destination equipment having a f requirement less than the flow rate in the selector h ducting, excess flow in the ducting being allowed to p outside the selector tube, pass through the annular se between the end of the ducting and static parts and vented to waste. 9. A selector valve as claimed in claim 8 in which destination equipment can be analytic equipment for exam a gas chromatograph.

Inventors: JESSOP ADRIAN, JESSOP, ADRIAN
Applicants: JESSOP ADRIAN, PROTEUS DEV LTD, JESSOP, ADRIAN, PROTEUS DEVELOPMENTS LIMITED
Application year: 1994
Main classification: F16K11
IPC codes: F16K11, G01N1